Historians of medieval medicine and science (and medievalists generally) often confront the questions: How well was a given treatise known in the Middle Ages, and who could have had access to it then? This project offers a new way to address those questions by drawing on the information contained in extant medieval library catalogues. The goal is to prepare and publish an inventory of books in medicine, biology, and Aristotelian natural science as they are listed in published medieval booklists. The inventory will include an introduction, an author/title list (about 4000 entries) which incorporates information about the medieval owners of the books, a list of medieval library catalogues (about 700-800 entries), a bibliography of published medieval booklists, and extensive analytical indexes. The PI will compile, sort, and typeset the inventory with the aid of an interactive computer system, UNIX (UNIX is a registered trademark of the Bell Telephone Laboratories), which is well suited to the tasks of data storage, text editing, word processing, sorting, and typesetting required by this project.